Voltage-gated L-type Ca2+ channels mediate Ca2+ signals that are essential for cardiac, endocrine, and neural functions. Although Cav1.2 is the predominant class of L-type channel in most tissues, Cav1.3 L-type channels play a major role in cardiac rhythmicity and neuronal excitability. Since small changes in Ca2+ influx can profoundly influence cellular excitability, factors that regulate Cav1.3 channels may control the balance between normal and diseased states of the nervous and cardiovascular systems. In screening for signaling molecules that specifically modulate Cav1.3, we discovered a novel regulation of these channels by interactions with proteins containing motifs known as PDZ-domains. The PDZ-protein, erbin, binds to the C-terminal domain (CT) of the 11-subunit (111.3) of Cav1.3 and dramatically enhances channel opening in response to depolarizing stimuli in a process termed voltage-dependent facilitation (VDF). A closely related protein, densin-180, also interacts with the 111.3 CT but does not influence VDF. Instead, densin-180 inhibits Ca2+-dependent inactivation of Cav1.3 and this effect depends on functional recruitment of calmodulin-dependent kinase II. Based on these findings, we hypothesize that Cav1.3 channels are fundamentally regulated by PDZ-protein interactions, which may diversify the signaling potential of these channels in different cell-types. The goal of this proposal is to characterize the molecular mechanism by which Cav1.3 channels are differentially modulated by such PDZ interactions, and the physiological significance of this regulation using molecular biology, immunochemistry, and electrophysiology. The proposed studies will clarify structure/function relationships and modulatory mechanisms that distinguish Cav1.3 from other L-type channels, which will broaden our understanding of the diverse physiological roles of Cav1.3 in regulating heart-rate, insulin secretion, and neural adaptations to psychostimulants. The long-term objective of this research is to gain molecular insights into the development of Cav1.3-selective drugs, which may provide novel and effective treatments for cardiac arrhythmias, diabetes, and drug abuse. PUBLIC HEALTH RELEVANCE: The proposed research will modulate voltage-gated Ca2+ channels. We will elucidate new structure/function relationships and modulatory mechanisms, which may be altered in diseased states of the cardiovascular and nervous systems.